1. Field of the Invention
This invention relates to a supply and return air plenum unit for duct air-conditioning systems adapted to be installed in a room of a house or building.
2. Description of the Prior Art
Self-contained room air conditioners are generally installed in a room of a house or building in the form of a wall unit, ceiling-hung unit, ceiling-built-in unit, or floor-mounted unit. Such a self-contained room air conditioner is relatively large in size as it contains relatively thick heat exchangers and a blower. The large-sized air conditioner projects into the room interior to a greater extent and hence is unsightly in appearance and also occupies a relatively large space in the room. Duct air-conditioning systems, unlike the self-contained room air conditioners, include a supply and return air plenum unit which is devoid of heat exchangers and a blower and hence can be constructed in a thin or flat structure. Two typical examples of such plenum unit are illustrated here in FIGS. 4 and 5 of the accompanying drawings. The plenum unit shown in FIG. 4 is installed in an offset portion of a ceiling and has a cooled/heated air supply outlet A defined in a vertical side wall and a return air inlet B defined in a horizontal bottom wall. The plenum unit shown in FIG. 5 is also mounted on an offset ceiling and has a cooled air supply outlet A1 defined in a vertical side wall, a heated air supply outlet A2 and a return air inlet B both defined in a horizontal bottom wall.
The first-mentioned plenum unit is disadvantageous in that since the cooled/heated air supply outlet defined in the vertical side wall directs heated air horizontally, the heated air is unlikely to flow in a downward direction. Consequently, a uniform temperature distribution is difficult to obtain when the air conditioning system is operating in a heating mode.
The foregoing difficulty never occurs in the latter-mentioned plenum unit in which heated air is blown off downwardly from the supply outlet A2 and cooled air is supplied horizontally from the supply outlet A1. However, a mode select door is required for selectively opening and closing the supply outlets A1, A2. With the mode door thus provided, this plenum unit is complicated in construction. Another problem is that, owing to a close arrangement of the heated air supply outlet A2 and the return air inlet B, heated air supplied from the supply outlet A2 tends to shortcut and returns through the air inlet B into the plenum unit before it is circulated in the room interior.